How to get sum of the values for every 10 rows? - vb.net

Question

Have a column in Datagridview (over 300 rows) and would like to get the sum of every 10 rows. There is no gap between the data in Column 1.
I just want to have the sum value for every 10th rows in the other column. What I have tried showing me the cumulative #s in each row!
Any help would be appreciated. Thanks so much!
C1 C2
2
3
4
6
5
3
5
7
6
5 46
8
9
4
7
5
2
1
2
5
4 47
1
2
6
.
.
.
Dim sum As integer = 0
For i = 0 To data1.Rows.Count - 1
sum += data1.Rows(i).Cells(0).Value
data1.Rows(i).Cells(1).Value = sum
If (i+1) = 10 Then
Sum = 0
Else
End If
Next

Answer 1

There are multiple ways, here is one example:
Loop over every row to sum, then on every 10th output sum and reset number.
For i = 0 To data1.Rows.Count - 1
sum += data1(0, i).Value
If i.ToString.EndsWith("9") Then 'since it starts at 0, 10th ends with 9 not 0
data1(1, i).Value = sum
sum = 0
End If
Next

Answer 2

Use LINQ to get the sum of each group of n rows
Private Function getSumsOfGroupsOfNRows(n As Integer) As IEnumerable(Of Double)
Return DataGridView1.Rows.OfType(Of DataGridViewRow).
GroupBy(Function(r) Math.Truncate(r.Index / n)).
Select(Function(g) g.Sum(Function(r) CDbl(r.Cells(0).Value)))
End Function
Test it with this
Dim n = 10
' adds numbers 1 through 100 in the datagridview, for testing
DataGridView1.Rows.AddRange(Enumerable.Range(1, 100).Select(
Function(r)
Dim row As DataGridViewRow = DataGridView1.Rows(0).Clone
row.Cells(0).Value = r
Return row
End Function).ToArray())
' get the sums in an IEnumerable(Of Double)
Dim sums = getSumsOfGroupsOfNRows(n)
' write into second column
For i = 1 To n
DataGridView1.Rows.Item(n * i - 1).Cells(1).Value = sums(i - 1)
Next